If you didn't replace the bushings in the trailing arms themselves I would at least take the time to check them out. It doesn't take too much time to verify if the poly-urethane bushings are good or not in the trailing arms and toe rods.

The cradle inserts only do so much to control that movement back there since they work in conjunction with the factory rear cradle bushings. Going with full poly-urethane replacement rear cradle bushings is always a better option and will control the rear cradle substantially better.